Method and apparatus for producing alternating currents



April- 51, 1927.

R. D. FAY ET'AIL IE'I'HQD AND APPARATUS FOR PRODUCINGALTERNATINGQCQRRENTS- Filed um 45 1922 4 sneets-shet 1 April 5, 1927. l,523,5

R. D. FAY- ET-AL METHOD AND APPARATUS FOR raonucms,ALTERNATINfi'CURRENTi Filed Marh 15 1922 4' She e fIs -Sheet 2 "3 I IWgfQ/TURS 5 va -W n A ril 5.1927.

R. D. FAY ET AL METHOD AND APPARATUS FOR PRODUCING ALTERNATING CURRENTSFiledMarch 15. 1922 4 Sheets-Sheet 5 May/T055 ww Patented Apr. 5, 1927.v

UNITED STATES 1,623,665 PATENT OFFICE.

RICHARD D. FAY, 0F NAHANT, AND EZEKIEL WOLF, OF BOSTON, MASSACHUSETTS,

ASSIGNORS, BY MESNE ASSIGNMENTS, T

TON, MASSACHUSETTS.

O HAMMOND V. HAYES, TRUSTEE, OF BOS- METHOD AND APPARATUS FOR PRODUCINGALTERNATING CURRENTS.

Application filed March 15, 1922. Serial No. 544,034.

ments of which are connected alternately tothe two poles of the sourceof current. In such an arrangement the difference of potential betweenadjacent segments is, during a considerable portion of the time, equalto the full voltage of the current source and at times may beconsiderably greater. It has been usual to complete the circuit by meansof brushes bearing upon the commutator which brushes are connected bywires with the condenser and the electro-magnetic device. It has beenfound by experience that such an arrangement has a very serious defectdue to the fact that when the commutator is revolved, arcs arefrequently formed between adjacent segments of the commutator.- Whensuch arcing occurs the commutator is quickly destroyed if notsufliciently protected by fuses. Attempts have been made to overcomethis defect by increasing the amount of insulation between the segmentsof the commutator. pedient has failed for therea on that after a littleuse portions of the brushes, which are Worn off by the revolvingcommutator, adhere to the surface of the insulating material betweensegments and produce a sufficiently conducting path to promote theformation of an are.

There is a second condition which also tends to produce flash overs andthe consequent destruction of the commutator. This condition ari-cs whenthe circuit is made or broken by a key, switch or similar deviceincluded in the circuit but independent in its operation from that ofthe pole changer. In practically every installation a key .or switch ofthis kind must be used and is essential in an oscillator circuit whenthe oscillator is used for producing code signals. Inall. sy tems ofthis kind hereto fore used there has been no means provided to restrictthe making or breaking of the circuit-through the action of this key tosuch Such an ex-- times as there is a minimum of current flowing acrossthe polechanger. The result has been that the circuit has been liable tobe broken at times of maximum current flow and consequently that flashovers are produced'at the pole changer with disastrous results. Thisditliculty has been fatal to the successful operation of a device ofthis kind when fairly large currents at fairly high potentials arereversed at the pole changer.

There is a third and very practical limitation to an arrangement of thiskind when the circuit and mechanisms are designed so that the condenserwill be fully charged during the time of contact of the brushes on thelive segments of the commutator or pole changer, with the object ofhaving the make and break of the circuit occur at a time when thecurrent across such contacts has ceased to flow. This limitation arisesfrom the impossibility of obtaining under such conditions thealternating current required to actuate the electro-magnetic device froma source of direct current having usual commercial voltages.

The above can best be illustrated by a practical case of the applicationof such an arrangement under usual commercial condi tions. In mostplaces 220 volts is the maximum voltage available from a direct currentsource. Let it be assumed that the electromagnetic device has aresistance of 9.5 ohms and an inductance of 1.25 milli-henries and thatit. is desired to produce an alternating current, through theelectro-magnetic device and a condenser in series with it, having afrequency of 500 per second. If the circuit is designed in such a waythat the condenser is fully charged before the circuit is opened at thepole changer, a condenser having about 25 microfarads must be employedand with it a power of about 550 watts is derived. The capacity waslimited to 25 microfarads in order to permit the condenser to be fullycharged before the circuit was broken. If a condcnser having a capacityof microfarads were used, the other constants of the circuit remainingas before, the power obtained by the electromagnetic device. would besomewhat more than doubled or would be about 1260 watts. In this lattercase, however, the current at the time of opening the circuit would beabout 6.7 5 amperes. In other words, if the power required for theoperation of the electro-magnetic device was more than 550 watts, if thevoltage of. the source Was limited to 220 and it it was required that nocurrent should be flowing at the time of making or breaking the circuit,then the system would be inoperative.

Our invention consists in the design of circuitmaking andcircuit-breaking mechanisms wherewith there is no possibility of arcingeven when a current of a reasonable strength is flowing. \Ve do notlimit ourselves to the condition that the electrical circuit containingthe condenser should have a time constant less than one half of'theperiod of the frequency desired but on the contrary so design the polechanger and key that they will care for current. of the strengthrequisite for the operation of the electro-magnetic device without thepossibility of flash overs or destructive arcing.

In our invention we have abandoned the use of a commutator as a polechanger and have substituted a device wherein the necessary contacts aremade and broken by the to and fro movements of two fairly large parallelconducting surfaces. The movements of these contact surfaces are sorapid and the opening between them is so great that there is onliability of an are following between the surfaces. Again we have-anranged the devicein such a way that the contacts with the positive mainof the supply circuit are all made in a compartment en tirely separateand insulated from a second compartment in which the contacts with thenegative main of the current supply circuit are made. This arrangementinsures complete immunity from the destructive arcing which has beeninherent inthe commutating devices heretofore employed. The thirdfeature which we have embodied in our invention is an electro-mechanicalarrangement by the'use of which a key can be used to transmit telegraphor code signals with the certainty that the operation of the key willeffect the making or breaking of the circuit onl when a minimum ofcurrent is passing an thereby eliminate the causes of the are which hasbeen fatal in the operation of earlier devices of-this kind. Furthermorewe employ a condenser of sufiicient capacity to obtain the requiredenergy from the available direct current source and in doing this dependupon the non-arcing properties of our polei" changer to carry thecurrent necessary to obtain'the required energy.

In the drawings accompanying the present specification Figure 1 showsdiagrammatically the simplest form.

Fig. 2 shows diagrammatically the circuit arrangement inthe exact formwhich has been embodied in the pole changer which we have Yound mostsatisfactory.

circuit arrangement. in its the mechanism used in connection with thekey or switch employed when thecurrent is interrupted for longer .orshorter intervals for producing code signals.

Fig.- 6 shows the circuit and arrangement of apparatus best suited toobtain an alternating current ot' nearly sinusoidal form.

n n I n Fig. 7 shows diagrammatically the circuit arrangement of thecomplete apparatus of Fig. 2 in its preferred form, there being added toa portion of this figure means whereby the circuit closers are heldagainst the cam and also means for preventing the circuit closers fromoperating.

In Fig. 1, 2 is a continuous current dynamo, storage battery or similarsourceof direct current. 3 and 4 are conductors used to carry thecurrent to the pole changer, 3 being connected with the positive poleand 4t with the negative pole of the source oi current. 5 and 6 areswitch arms connected with the positively charged conductor 3 and 7 and8 similar arms connected with the negative conductor 4. 9 and 10 arefixed contacts with which switch arms 5 and 8 can engage. Contacts 9 and10 are connected with one side of condenser 12 by conductor 11. 13 and14 are fixed contacts with which switch'arms 6 and 7 can engage.Contacts 13 and 14 are connected with one end of the secondary windingof electro-magnetic device 15, shown as a Fessenden oscillator (U. S.Patent No. 1,167,366) by conductor 16. The other end of the secondarywinding is connected with conductor 17 and by it with the other side ofcondenser 12'. The switch arms 5, 6, 7 and 8 are actuated by cams, to bedescribed later in detail, in such a way that when 5 and 9 are incontact 7 and 14 will also be in contact and 6 and 13 as well as 8 and10 will be broken. As the cams revolve the contacts 5-9, and 714 willbebroken and later 613 and 8-10 made. The shape of the-cam or camsis's'uch as to give the desired relative periods of open or closedcircuit at the usual contact points.

{To obtain a complete cycle of the alternat- Ill] ing current thesequence of making and [Ch of the four when lower frequencies aredesired, we prefer to use for higher frequencies the arrangement showndiagrammatically in Fig. 2. This arrangement is in principle identicalwith that shown in Fig. 1 except that two more switch arms 18 and 19 areconnected with the positive power main and two additional switch arms 20and 21 are added to the negative mains. These swith arms engage contacts22 and 23 and 24 and 25-respectively. The contacts 22 and 25 areconnected with the wire 11 leading to one side of'the condenser andcontacts 23 and 24 are connected with the electro-magnetic device andthe other side of the condenser by wire 16 as before.

A practical means embodying our invention is shown in Figs. 3, 4 and 7,Fig. 3 showing at 32 one of the stationary plates carrying themechanism, Fig. 4 showing in elevation the plate structure, and Fig. 7illustrating the various circuits and the means for operating them, allin diagrammatic form. 28 is a motor having its casing mounted on a base29 and driven from" any source, 281 bein its leads. Brackets 291supported bythe ase 29 carry at their outer ends plates 32, 34. 33 isthe motor shaft which passes through the plates .32, 34 and carries ateach end a cam 26 which is thus rotated by the motor 28. The cams 26 areidentical in shape and the parts operated by them and their electricconnections are the same; As shown each cam vhas nine projections 27each of which from the beginning to the limit of its rise subtendsan'arc of 30 while the low space 271.between the highest limit of oneprojection and the beginning of the rise of the next projection subtendsan arc of 10. In 'Fig. 3 is shown the plate 32 with the various partsattached. Around the cam 26 are arranged switch arms 5, 6, 18 and 19.The arms 7, 8, 20 and 21 are ai ranged aroundthe corresponding cam atthe other end ofthe shaft 33. Describin the set shown in Fig. 3, eacharm is pivote to the plate 32 and insulated therefrom and has a finger51, 61, 181 and 191 which engages the edge of the cam, but is insulatedtherefrom. Each arm on plate 32 is electrically connected with the wire3 and when its finger is riding over the low portion only of the cam,may make contact with 9, 13, etc., thus closing the circuit through wire16. The switch arms on plate34 are arranged in all respects like thoseon plate 32, but are connected with wire 4, and the two cams arearranged on- :haft- 33 so that arms on the two plates operatesynchronously (see Fig. 7). 'Thus'when one of the arms on plate 32 makescontact a corresponding arm on plate 34 also makes contactsii'nultaneously and the circuit is closed througlfthe wires 11 and 16and through the device'15. This arrangement allows the contacts to besomewhatbroad rather than mere identical at the two ends of the shaft 33and are set on that shaft so that two switch arms will be operatedsimultaneously, it will be seen that both positive and negative lineswill be closed momentarily at the same instant.

This multiple arrangementofgswitch arms and projecting cam surfacepermits the cam as a whole to be revolved at a lower speed than wouldotherwise be required to obtain a given frequency of alternatingcurrent.

In Fig. 7 plate 32 is shown and on it are the parts shown in Fig. 3,these two views of 32 being substantially identical. The plate 34 showsarms 7, 8, 20 and 21 corresponding," respectively, to arms 5, 6, 18 and19 on plate 32; Each arm has fingers 71, 81, 201 and 210 correspondingwith the fingers 51, 61, 181 and 191-. The contacts-on 34 are numbered14, 10, 24 and 25 corresponding with the contacts 9, 13, 22 and 23. Itwill be seen, for exam le, that when contact is closed by the arm at 14,thus connecting the line 4' with the line 16, contact 9 will be closed,thus connecting the arm 5 with the line 11 and the line 3.

In order to overcome the danger of arcin arising from breaking thecircuit when sen 1 ing signals by the use of a key or switch due to thecontact being made at a time of maximum current flow, the arrangementshown" enlarged in Fig. 5 as well as in Figs. 3, 4 and 7 ,is employed inconnection with each switch arm. Each switch arm carries a spring latchmember 361 adapted to engage with a latch member 36 mounted'on the endof a spring 40 attached to the plate 32 so that when the switch arm hasbeen forced back by a pro jection- 27 of cam 26v the latches willnormally engage and hold the switch arm from touching its associatedcontact until released. An'electromagnet 35 is located to control theportion of the spring 40 which acts as the armature of itselectroanagnet 35. These electro-magnets preferably on both plates 32and 34 are connected in circuit with a hat' tery 38 and key 39 in such away that. when key 39 is depressed and the local circuit 'com pleted,all the electro-magncts will be encrgized and the latches on the armsreleased so that whenever an arm is in proper relabe in position to'catch and hold the switch arms as the switch arms are forced back by thecam. In this way it is impossible to have the main current supplycircuit broken by the pole chan er except when the current is less thana de ite value.

It will be understood that'the plate 34 in fact carries parts identicalwith the abovenamed parts constructed and operating in the same way.

In Figs. 6 and 7 are shown diagrammatically a modified form of thecircuit shown in Fig. 2. We have found that this latter arrangement ofcircuit and apparatus may be made to produce a current curve more nearlyapproaching the sinusoidal formobtainedfrom alternating currentgenerators such as have been commonly used heretofore.

pedance coil of proper inductance Z and a proper resistance 1' areconnected in series with the electromagnetic device, and a secondcondenser C, of smaller capacity than C, is connected in shunt about theelectromagnetic device and auxiliary inductance. Z-.

by wires 401 and 41.

We have found that with the above arrangement of apparatus and byproperly proportioning the-capacitiesof thecondensers to the resistancesand inductances of the electro-magnetic elements connected in thecircuit shown in Figi '6 and by the use] pass out through openings inplate 32 and nected in a manner which will be understood by one skilledin the art.

their respective -circuits are suitably con- What we claim as ourinvention is 1. In combination, a member adapted to be operated byalternating current and having a lead from each side-thereof, a directcurrent source having a lead from each side thereof, a pole changercomprising a motor,two cams rotated thereby, two groups of switch arms,one group being connected to the positive lead from said source and theother to the said contacts being connected to one sideof said member andthe rest to the other side of said member, each cam being shaped to vallow one switch arm of each group at a time to engage its contact andsaid cams being arranged whereby both cams will operate one switch armof both ously.

- 2. A- pole changer com rising a motor, a cam rotated thereby, an eectric circuit comgroups simultane- In this second arrangement anauxilliary imprising switch members and contacts therefor,

said cam being adapted to control the engagement of said switch memberswith their contacts, latch members adapted normally to hold said switchmembers out of contact with said cam and said contacts, and means forreleasing said switches from said latches comprising electro-magnets, acircuit, a

current source comprising two-grou s ofswitch arms, one-group connectedwit one pole of a direct current source and the other group with theother "ole of the same source, and cards so arranged with relation tosaid switch arms that two switch arms, one from each group will at thesame time be allowed to make and break the .circuit at the contactsassociated therewith, and" that each switch arm of each group will inturn bear upon the contact with which it is associated.

4. In a pole changer for producin in a circuit alternatin current froma'direct'current source, switc ing means, means for openrent source,switching means comprising two sets of arms, each arm of oneset beingconnectible to a corresponding arm of the other set, means for causingconnections between different pairs of arms to be operatedconsecutively, means -for retaining said'switching means when opened,and means for releasing said retaining -means whereby the circuit can bemade and broken only at times of minimum current flow.

6. In a pole. changer for producing a circuit alternating current from adirect current sourceincluding a circuit, switching means, means foropening and closing said switching means, means for retaining saidswitchin means open comprising latches one mem r of each of, which isattached to one member of said switch, the other memberthereofbeing'adapted to. engage said first member when said first memberis in rei tracted position and hold it, and means for releasingsaidaetaining means comprising an electro-magnet whereby the directourtimes of minimum current flow.

rent circuit can be made and broken'only at

